The new findings appear to contradict claims that Hitler lost a testicle to a shrapnel injury in the First World War.

In an account that was only discovered in 2008, Franciszek Pawlar, a Polish priest and amateur historian, claimed a German army medic who treated Hitler after the incident told him about the injury.

They also appear to contradict the account of Hitler’s childhood doctor, Eduard Bloch, who told American interrogators in 1943 the Fuhrer’s genitals were “completely normal”.

In very rare cases, cryptorchidism can develop later in life.

A practising Jew, Dr Bloch stayed in Austria under Hitler’s personal protection until 1940, when he emigrated to the US.

The Soviet autopsy carried out on Hitler’s remains in the Fuhrerbunker after the fall of Berlin found that one testicle was completely missing — although, curiously, it recorded the left testicle as absent.

If Hitler did have an undescended testicle, it could explain why he had no children, as it is often linked to reduced fertility.

It would not necessarily have affected the Fuhrer’s sex life, as there is not generally a link to impotence.

The popular song emerged in 1939 and is thought to have been written by a publicist for the British Council, which was tasked with helping build propaganda that would damage the Nazis.

The commonly-recalled version is an adaptation of the original, which ran: “Göring has only got one ball, Hitler’s [are] so very small, Himmler’s so very similar, And Goebbels has no balls at all.”

During the event, a total of 33 Spitfires, Hurricanes and Bristol Blenheim bombers flew from Goodwood Aerodrome in West Sussex before dispersing across wartime airfields over the South of England.

A Kensington Palace spokesman said: “Prince Harry has chosen this photograph with Battle of Britain veteran Tom Neil for his Christmas card.

“He considered it a great honour to meet Tom during the Battle of Britain flypast in September. It was one of his most memorable moments of 2015.”

The picture was taken by the Press Association’s veteran royal photographer John Stillwell.

Harry gave up his seat to ensure veteran Tom ‘Ginger’ Neil and two wounded servicemen could still take part in the biggest gathering of Battle of Britain aircraft since the Second World War.

Around 40 Spitfires, Hurricanes and Bristol Blenheim bombers are flying in formation from Goodwood Aerodrome in West Sussex before dispersing across wartime airfields over the South of England.

The Prince was due to have a seat in one of four two-seater Spitfires taking part in the flypast. But when one of the vintage aircraft developed mechanical problems, he decided to step aside to ensure the event’s special guests would still get to fly.

His spokesman said he wanted to make sure that Mr Neil would still be able to take part. And he wanted to ensure that a former para and an RAF corporal who won places on a Spitfire scholarship training programme were also still able to take part in the display.

“As a nation, internment weakened us all. It is a tragic reminder of what happens when we allow fear and hysteria to trump our values.

“Historians and leaders across the political spectrum agree internment was a grievous mistake and a violation of basic human rights. It detracts from the amazing efforts by my grandfather to rescue our economy and build the foundation of America’s great middle class.”

Earlier this week, Mr Trump compared his plan to Roosevelt’s classification of thousands of Japanese, Germans and Italians living in the US during the war as “enemy aliens”.

He said Roosevelt, one of America’s greatest presidents, was “highly respected by all”, and then stated: “Take a look at presidential proclamations, what he was doing with Germans, Italians and Japanese, because he had to do it.”

The billionaire businessman made the proposal, that Muslims including would-be immigrants, students and tourists, should be blocked from entering the country, in the wake of the deadly shootings in San Bernardino, California, last week by a married couple inspired by Islamic State militants.

An authentic antidote to the high jinks of Messrs Clarkson and co, he went on to renovate a narrow boat, reconstruct a beached Spitfire and investigate Industrial Revolution technology. And most eye-catchingly of all, in Speed with Guy Martin on Channel 4, he attempted to break a wacky series of hair-raising records on land, water, ice and in the air.

Martin’s grandfather was conscripted by the Nazis in 1941. No one in the presenter’s family had a clue

One of the most impressive of his feats was breaking the British record for outright speed on a bicycle – he hit an extraordinary 113 mph by using the slipstream created by a specially-modified lorry. (He has since said that he wants to reach 200mph.)

He also broke the British hovercraft speed record on Loch Ken, in Dumfries and Galloway, and the speed record for a toboggan, although, when he attempted to break the world record for the hovercraft, a change in wind direction saw him fly 100ft into the air at 76 mph, damaging the craft and forcing Martin to abandon ship.

A show on Channel 4 next year will see him attempting the world speed record for the Wall of Death, the epic fairground stunt that involves riding a motorcycle around a vertical wall. Martin – who, on top of his crash this year, broke his back and eight ribs in 2010 in a crash on the Isle of Man – is fearless.

But, outside of these adrenalinefuelled pursuits, he has a simple life. Diagnosed with Asperger’s Syndrome, he is reluctant to become a full-time TV presenter, doesn’t even own a television (or a smartphone) and, while out on location, often spurns the hotel to sleep in his van with his dog. But it’s exactly this combination of eccentricity and humility that makes him so popular with viewers.

What choice did he have? You look at the bare bones of it, that’s all he could have done. I’d have done the same

Guy Martin

Knowing a good thing when they see one, Channel 4 persuaded him earlier this year to film a travelogue. Our Guy in India took Martin on a 1,000-mile motorbike trip around the country. And now he has made his most personal documentary yet.

“After Our Guy in India they asked me if I wanted to shoot abroad again. I said, ‘I’m not a big holiday person but I’ve always wanted to go to Latvia. Just to find out what it’s like.’” Researchers delved a little deeper and found that there was a much more compelling programme than a bog-standard portrait of modern Latvia.

It turned out Martin’s late grandfather, Walter Kidals, whose original first name was Waldemars, came from Latvia and had been conscripted by the Nazis in the Second World War.

He had then spent two years in a Belgian prisoner-of-war camp, before arriving in Hull as a refugee in 1947. No one in Martin’s family had a clue. Martin’s main memory is of a man who liked his shed and “didn’t say much”.

“His English wasn’t the best,” he says. “He could get his point across. He was just different, just the way he ate and the way he drank his tea. He’d mix anything with anything.” Walter shared so little that even his wife Lill, now 92, had no idea that he was an orphan.

Like tens of thousands of Latvians, when Germany occupied the country in 1941, Walter was offered a choice: fight for the Nazis, or face death. At 80,000, the Latvians formed one of the largest national groups of Nazi conscripts. What would his grandson have done? “You had no choice,” he says. “What other option was there? You look at the bare bones of it, that’s all you could have done. I’d have done the same.”

After the war Latvian soldiers were exonerated by the Nuremberg trials and surviving conscripts were allowed to settle in the US and Britain as political refugees.

For Walter, there was no option of going home to a country which was now part of the Soviet Union. To simulate the kind of welcome his grandfather would have received, Martin visited a former prison which offers a quasitotalitarian experience in which curious tourists are brutalised and shouted at in Russian.

“There was no friendly atmosphere at all. We didn’t have a chat beforehand. They wouldn’t shake my hand, told me to sign this form, and from there on it was a bit of a battering. I genuinely was bloody scared.”•• •

In Our Guy in Latvia Martin once more reveals himself as a hugely likeable one-off. His down-to-earth aura, and eagerness to throw himself into anything, would have brought a welcome injection of unmediated spontaneity to Top Gear, so it is all the more regrettable that he turned down Chris Evans’s invitation to join. Instead, he’s sticking to fixing lorries while nipping off to make programmes for Channel 4. “It’s not for me,” he says. “I’m sure it would have been good for a pay cheque but I think I’ve got the best job in the world.

“Television opens up some bloody great doors. That’s the plus. The minus is the attention it brings. It is a bit of a pain now just doing a few hours of television a year. I don’t want to be famous. And that would have been a whole new level if I had gone and done Top Gear. It would be just stepping into Jeremy Clarkson’s shoes.

“What we do on Channel 4 is like our own version. If they keep coming up with interesting ideas I’ll do them. If they come up with crap ideas I’ll just go to work.”

The young airman never returned, although the story of valour and heroism behind the medal should help raise a huge sum for WaterAid when it is auctioned next week.

David Kirk, of auctioneers Morton & Eden said the lot, which includes a letter from Hopgood’s commander informing his mother of his death, was “undoubtedly” one of the most iconic Distinguished Flying Cross medals to be auctioned in years.

He said: “Flight Lieutenant Hopgood’s family has agonized over the decision to part with the medal but feel that John Hopgood himself would approve.

“He was evidently a very thoughtful and idealistic young man who, we believe, would be glad to know that the proceeds from the sale of his medal will go towards the building of a much-needed sand dam to benefit thousands of people in Uganda.

“The new dam will form a fitting memorial to Hopgood’s heroism and self-sacrifice on the Dambusters’ mission, of which his family can be duly proud”.

Thomas Benn, of WaterAid, said: “WaterAid is delighted that the family of Flt Lt John Hopgood will pay tribute to him through supporting our lifesaving work. “

“The new dam will form a fitting memorial to Hopgood’s heroism and self-sacrifice on the Dambusters’ mission, of which his family can be duly proud”

David Kirk, of auctioneers Morton & Eden

Born in the village of Hurst, Berkshire, the pilot was educated at the prestigious Marlborough College, known today as the secondary school of the Duchess of Cambridge and Samantha Cameron.

As war broke out he was due to go to Corpus Christi College Cambridge to read law, but instead joined the Royal Air Force.

Despite his age he became a respected airman for his “considerable courage and cool nerve” while flying perilous sorties behind enemy lines.

He received the Distinguished Flying Cross in October 1942 and a few months later, in January 1943, he received his second award Bar.

Hopgood was selected to fly with 617 Squadron, who on the night of May 16-17 1943, executed Operation Chastise.

As part of Formation No 1 he followed Wing Commander Guy Gibson in a swoop on the Mohne Dam in West Germany.

Despite receiving serious wounds on the approach, the young airman flew low enough over the dam for the “bouncing bomb” to strike and destroy a hydroelectric power station.

Then, in a final act of selfless valour, he manoeuvred his Lancaster to gain enough height for his crewmen to bail out.

Those who survived were decorated and Gibson received the Victoria Cross.

The medal is being sold by his family in an auction on Tuesday December 15 at Morton & Eden Ltd, Nash House, St George Street, London.

An authentic antidote to the high jinks of Messrs Clarkson and co, he went on to renovate a narrow boat, reconstruct a beached Spitfire and investigate Industrial Revolution technology. And most eye-catchingly of all, in Speed with Guy Martin on Channel 4, he attempted to break a wacky series of hair-raising records on land, water, ice and in the air.

Martin’s grandfather was conscripted by the Nazis in 1941. No one in the presenter’s family had a clue

One of the most impressive of his feats was breaking the British record for outright speed on a bicycle – he hit an extraordinary 113 mph by using the slipstream created by a specially-modified lorry. (He has since said that he wants to reach 200mph.)

He also broke the British hovercraft speed record on Loch Ken, in Dumfries and Galloway, and the speed record for a toboggan, although, when he attempted to break the world record for the hovercraft, a change in wind direction saw him fly 100ft into the air at 76 mph, damaging the craft and forcing Martin to abandon ship.

A show on Channel 4 next year will see him attempting the world speed record for the Wall of Death, the epic fairground stunt that involves riding a motorcycle around a vertical wall. Martin – who, on top of his crash this year, broke his back and eight ribs in 2010 in a crash on the Isle of Man – is fearless.

But, outside of these adrenalinefuelled pursuits, he has a simple life. Diagnosed with Asperger’s Syndrome, he is reluctant to become a full-time TV presenter, doesn’t even own a television (or a smartphone) and, while out on location, often spurns the hotel to sleep in his van with his dog. But it’s exactly this combination of eccentricity and humility that makes him so popular with viewers.

What choice did he have? You look at the bare bones of it, that’s all he could have done. I’d have done the same

Guy Martin

Knowing a good thing when they see one, Channel 4 persuaded him earlier this year to film a travelogue. Our Guy in India took Martin on a 1,000-mile motorbike trip around the country. And now he has made his most personal documentary yet.

“After Our Guy in India they asked me if I wanted to shoot abroad again. I said, ‘I’m not a big holiday person but I’ve always wanted to go to Latvia. Just to find out what it’s like.’” Researchers delved a little deeper and found that there was a much more compelling programme than a bog-standard portrait of modern Latvia.

It turned out Martin’s late grandfather, Walter Kidals, whose original first name was Waldemars, came from Latvia and had been conscripted by the Nazis in the Second World War.

He had then spent two years in a Belgian prisoner-of-war camp, before arriving in Hull as a refugee in 1947. No one in Martin’s family had a clue. Martin’s main memory is of a man who liked his shed and “didn’t say much”.

“His English wasn’t the best,” he says. “He could get his point across. He was just different, just the way he ate and the way he drank his tea. He’d mix anything with anything.” Walter shared so little that even his wife Lill, now 92, had no idea that he was an orphan.

Like tens of thousands of Latvians, when Germany occupied the country in 1941, Walter was offered a choice: fight for the Nazis, or face death. At 80,000, the Latvians formed one of the largest national groups of Nazi conscripts. What would his grandson have done? “You had no choice,” he says. “What other option was there? You look at the bare bones of it, that’s all you could have done. I’d have done the same.”

After the war Latvian soldiers were exonerated by the Nuremberg trials and surviving conscripts were allowed to settle in the US and Britain as political refugees.

For Walter, there was no option of going home to a country which was now part of the Soviet Union. To simulate the kind of welcome his grandfather would have received, Martin visited a former prison which offers a quasitotalitarian experience in which curious tourists are brutalised and shouted at in Russian.

“There was no friendly atmosphere at all. We didn’t have a chat beforehand. They wouldn’t shake my hand, told me to sign this form, and from there on it was a bit of a battering. I genuinely was bloody scared.”•• •

In Our Guy in Latvia Martin once more reveals himself as a hugely likeable one-off. His down-to-earth aura, and eagerness to throw himself into anything, would have brought a welcome injection of unmediated spontaneity to Top Gear, so it is all the more regrettable that he turned down Chris Evans’s invitation to join. Instead, he’s sticking to fixing lorries while nipping off to make programmes for Channel 4. “It’s not for me,” he says. “I’m sure it would have been good for a pay cheque but I think I’ve got the best job in the world.

“Television opens up some bloody great doors. That’s the plus. The minus is the attention it brings. It is a bit of a pain now just doing a few hours of television a year. I don’t want to be famous. And that would have been a whole new level if I had gone and done Top Gear. It would be just stepping into Jeremy Clarkson’s shoes.

“What we do on Channel 4 is like our own version. If they keep coming up with interesting ideas I’ll do them. If they come up with crap ideas I’ll just go to work.”